Chris,
RAID 5 gains more slowly in performance once you get to 6 or more disks
based on some of the benchmarks that I have seen. RAID 50 is generally
better with using 8 and more drives. In your case though, losing a drive
would cause a performance hit in RAID 50, though I'm pretty sure that it
should perform better in optimal condition and 8-10+ drives than RAID
0+1 unless you are hitting the limits of the RAID card's processor. Your
database needs are also very different than a mail server, and much more
difficult to deal with.
One thing that also might not be considered here is that while you do
get more capacity with RAID 5, you don't need to use that capacity and
in turn you can enhance performance considerably by only using part of
the drives, a practice called "short-stroking". The outside edge will
read and write at around double the speed of the inner-most edge, so if
you only use the outer half of the drives (which represents around 2/3
of the capacity) , you can increase the average performance of each
drive by about 20%-25%. This also goes up over 50% increases depending
on how much you use. Seek times also improve since the heads have to
travel less. You can do this with all RAID levels, but the benefit of
the extra capacity in RAID 5 can be turned into additional performance
if it isn't needed by just simply keeping your partition sizes down.
Matt
Christopher Checca wrote:
In my experience running on MS SQL server databases and AcuODBC (AIX UNIX)
databases, with RAID arrays have 8 to 16 drives with 1TB to 4TB of total
storage.
RAID 0+1
In normal operation it performs slightly better (50 to 80 Mb sustained
throughput better) than RAID 5 array with the same drive sizes and number of
drives.
Upon failure the RAID 0+1 continues without any loss of performance, where
RAID 5 losses about 50% of its performance (total throughput).
NOTE: RAID 0+1 is not RAID 10 (1+0)
You are correct RAID is not backup … it’s continued operation upon
a drive failure.
In my environment performance during a loss of a drive is most important …
the cost pre GB is not the major consideration.
Christopher Checca
Packard Transport, Inc.
IT Department
24021 South Municipal Dr
PO Box 380
Channahon, IL. 60410
815 467 9260
815 467 6939 Fax
[EMAIL PROTECTED]
www.packardtransport.com
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Robert E. Spivack
Sent: Thursday, February 23, 2006 9:06 PM
To: [email protected]
Subject: RE: [IMail Forum] New Server Specs
So why use RAID 0+1 ? Costs more, performs less, adds only slightly more
reliability (data should be backed anyone and no RAID should be fully
trusted)
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